Mitigating hydrogen engine knock through water injection: a numerical study on hydrogen autoignition

Current engineering research is considering the utilisation of hydrogen internal combustion engine (H2 ICE) technology, offering close to zero engine-out emissions, as a pathway towards decarbonisation. This project aimed to analyse different hydrogen combustion parameters and autoignition conditions in internal combustion engines. A two-zone model within ANSYS Chemkin-Pro was adapted to assess hydrogen's chemical and thermodynamic processes under various conditions, predicting autoignition inside a single combustion chamber with a displacement of 1100 cm3, designed to represent a single cylinder of a widely used inline-6 engine architecture. This helped examine and apply the current engine knock reduction solutions for conventional fuel internal combustion engines, including water injection, filling the gap in alternative fuel knock research. The findings sugg est that lean mixtures are less prone to knock, while rich mixtures exhibit increased autoignition tendencies. Moreover, stoichiometric operation shows signs of knock, which can be mitigated by integrating water injection. Three cases were tested, corresponding to water content levels of 2%, 3%, and 4% in the oxidiser, based on mole fraction. The results indicated that 12 mg/cycle and 18 mg/cycle injections effectively reduced knock onset, with complete elimination achieved at 24 mg/cycle, enabling safe operation.